My biggest pet peeve is inconsiderate people, but there's a close second, too. People who feel entitled to things that they're not at all entitled to. Here's an example.
I was at the gas station this morning, as I am every morning, getting my Polar Pop for my caffeine for the day. As I opened the door to leave, I checked behind me (as I always do) to see if anyone was back there so I could politely hold the door for them. Sure enough, a fat lady carrying a couple bags of chips and a few candy bars was making her way out, a couple dozen feet behind me or so.
I held the door with a smile in that 4 degree weather as she waddled toward me. We made eye contact, and she gave me a head-nod, sort of saying "yeah, I see you holding the door", as she dug in her purse for her keys. After a few seconds of her moving at a snail's pace and me standing out in the freezing cold, I thought "ya know what, forget it." And I let the door slam. As I walked away from the door, I saw her scurry toward it, trying to catch it before it slammed shut. She gave me a dirty look as I climbed into my car, but all I could think the entire time was "scurry, you fat cow! When someone is holding the door, you SCURRY!"
Then I thought of a few other things. Like how I only "knew" this lady for about 10 seconds and I already hated her. She was inconsiderate. Inconsiderate of me, standing there holding the door for her in the freezing cold. Inconsiderate of the rest of the line as she took her time getting out of their way. Inconsiderate to the check-out ladies who got a nice cold blast of air as I kept the door propped open for far too long, waiting for her.
I knew she had an undeserved sense of entitlement because of the slow walk towards the door, like I simply HAD to keep that door open no matter how long it took her to get there. And by the dirty look she gave me, like how DARE I not fulfill my obligation by letting the door shut.
I'm also pretty sure she'll tell her own version of this story about the guy at the gas station who slammed a door in her face as she tried to hurry out. Oh well.